The water felting of dilute aqueous dispersions of mineral wool and lightweight aggregate is a well-known commercial process for manufacturing acoustical ceiling tile. In this process, an aqueous slurry of mineral wool, lightweight aggregate, cellulosic fiber, binder and other ingredients, as desired or necessary, is flowed onto a moving foraminous support wire, such as that of a Fourdrinier or Oliver mat forming machine, for dewatering. The slurry may be first dewatered by gravity and then dewatered by vacuum suction means to form a basemat. The wet basemat is then pressed (with or without the application of additional vacuum) to the desired thickness between rolls and the support wire to remove additional water. The pressed basemat is then dried in heated drying ovens, and the dried material is cut to the desired dimensions and optionally sanded and/or top coated, such as with paint, to produce acoustical ceiling tiles and panels.
Mineral wool acoustical tiles are very porous which is necessary to provide good sound absorption. The prior art (e.g. U.S. Pat. Nos. 3,498,404; 5,013,405; 5,047,120 and 5,558,710) also discloses that mineral fillers, such as expanded perlite, may be incorporated into the composition to improve sound absorbing properties and to provide lightweight acoustical tiles and panels. When used in water felting processes, compositions containing expanded perlite require a high level of water to form a workable aqueous slurry. It has been found that conventional expanded perlite (e.g. perlite having a density of from about 3 to 5 pounds per cubic foot) holds and retains a very high level of water within its structure. Laboratory tests show that such conventional expanded perlite can retain as much as 10 times its weight in water. Perlite, treated in accordance with the present invention, retains much less water. Typically less than half of the normal amount of water is retained by the perlite particles. The use of an expanded perlite, treated in accordance with the present invention, allows the formation of a mat containing significantly less water. These factors allow the production of acoustical tiles on conventional equipment at higher speeds.
It is an object of this invention to provide an acoustical tile composition containing expanded perlite which may be more efficiently fabricated into acoustical tiles and panels in a water felting process wherein the conventional expanded perlite is treated to reduce the tendency of the perlite to retain water.
It is a further object of this invention to provide an acoustical tile composition containing expanded perlite which may be more efficiently fabricated into acoustical tiles and panels in a water felting process wherein the conventional expanded perlite is treated with a silicone compound to reduce the tendency of the perlite to retain water.
It is a still further object of this invention to provide an acoustical tile composition containing expanded perlite which may be more efficiently fabricated into acoustical tiles and panels in a water felting process wherein the conventional expanded perlite is treated with a silicone compound having at least some hydrophilic functionality. This hydrophilic functionality on a silicone compound provides a particle that does not retain water while maintaining a degree of wettability that permits the treated perlite to be mixed into the standard water-felted furnish. These and other objects will be apparent to persons skilled in the art in view of the description that follows.